The qualitative and quantitative detection and identification of pollutants in multiuse drink bottles, such as e.g. wood preservatives, multipurpose cleaners, oils, petrol, pesticides and other toxic substances, is an important problem for reasons of product loyalty, protection of human life, taste quality of drinks, environmental protection and the problems linked with the disposal of toxic substances. This problem more particularly occurs in connection with multiuse plastic bottles, e.g. those made from polyethylene and polycarbonate, because as a result of high diffusion coefficients the pollutants diffuse into the bottle walls. The pollutants are consequently not completely removed during the washing process and after refilling the bottle can diffuse back into the drink and have a negative influence on its taste.
The prior art does not solve the problem of detecting such pollutants in non-disposable or multiuse bottles. All that is commercially available is machines which, using photoionization detectors, which after removing a sample from the gas area of the bottle partly ionize this sample with ultraviolet radiation and measure the ion current occurring in an electric field, attempt to conclude whether any pollutants are present. However, as such photoionization detectors also detect harmless gases, such as e.g. water vapor, carbon dioxide, methane, etc., the ionization energy of the ultraviolet light must be so low that the substances are not indicated. As a result harmful pollutants, such as e.g. methanol, oils, diesel, ammonia, etc. also fail to be detected.
In addition, due to the high bottle capacities in the drinks industry of up to 50,000 bottles per hour and the resulting short measurement times per bottle, it is frequently necessary to have multiple sensor arrangements with up to forty sensor systems, which leads to unacceptably high costs for the overall system.
U.S. Pat. No. 4,858,767 refers to the use of mass spectrometers. However, such systems are only suitable to a limited extent for solving the problem, because the ionization necessary for mass selection also leads to a fragmentation of the molecules, so that the ionization products comprise other molecular compounds than the actual substances to be originally analysed. This more particularly occurs with the large molecules which appear in drinks or beverages, so that the measurement does not allow clear conclusions to be drawn regarding the toxicity or non-toxicity of the particular gaseous mixture. Both methods can lead to a contamination of the sensor, so that its effectiveness is reduced.
The solution to the problem proposed by U.S. Pat. No. 4,858,768 is that a bottle should be eliminated from the filling process if there are divergences compared with the pure drink. However, this is unacceptable for economic reasons, because divergences already exist if non-toxic substances are admixed with the drink, so that unobjectionable bottles are removed from the process.
It has generally already been proposed to investigate the gaseous content of returned drink bottles by infrared spectroscopy. However, conventional infrared spectroscopy does not generally have the desired resolution and is time-consuming, a high time requirement particularly resulting from the fact that a very large wavelength range must be covered due to the lack of high resolution.
WO-88/0862 proposes (IR) spectroscopy, without specifying the evaluation. Apart from the aforementioned disadvantages, an analysis of the total spectrum is too time-consuming or expensive. To the extent that spectroscopy in the near infrared between 1.1 and 2.5 .mu.m is proposed, it has been found that this range is not sufficiently critical, i.e. the spectra in this range do not provide valid information, because they are not material-specific. In addition, the detection sensitivity in the near infrared is extremely low. Moreover, the necessary evaluation by regression analysis is time-consuming.
Admittedly, in the case of a Fourier transformation spectrometer detection takes place more rapidly, however, for the evaluation it is necessary to have expensive computers, which are economically unacceptable for the intended use, and the procedure is too slow for conventional drink filling plants due to the spectrum evaluation and comparison with specimen spectra.